Variable condenser



July 10, 1928. 1,677,020

E. G. DANIELSON VAR IABLE CONDENSER Filed May 24, 1926 FEEQUCNCY 5) 462 o ANS/I14? MOT/ON GOA/7204 Patented July 10, 1928.

UNITED STATES 1,677,020 PATENT OFFICE.

ERNEST G. DANIELSON, OF- SAN FRANCISCO, CALIFORNIA.

Application filed May 24,

This invention relates generally to devices intendcdto be used for tuning 'an electrical circuit, particularly" ,gresonan't circuits .em'- ployed in radioreceiving sets.

Resonant circuits are commonly ,tuned with variable ccndenser: s 'comprising a'plu rality of relatively movable electrodes. In present day radio apparatus it is customary tocmploy a'given'standard inductance with a condenser of a certain ma imumca pacitance whereby the broadcast wave length range may .be efficiently covered within the range of movement otthe condenser. Sinc e licensed broadcast stations are evenly spaced along the frequency scale, it is desirable for the condenser to have a straight line frequency characteristic; that is, fortheresonance frequency 0f thecircuit to vary as a linear function of angular movenierito'f the condenser .control sl1 aft. To accon'iplish' this result :it has .been previously proposedto shape the plates of the electrodes 59 that the condenser approaches its minimum pacitance, ,a. given amount of relative "movement between the electrodes will cause relatively small variations in capacitance. This: method is objectionable since'it results in electrodefplates of lpeculiaroutline which are ditficult tomonnt and expensive to manufacture. p

Another disadvantage with prior types of condensers has been the'irinability to vary their minimum capacitance without making a corresponding chan e in maximum capacitance. lVhen a com enser is incorporated with a receiving set it is desirable to have some means for varying the resonance frequency of the circuit corresponding to the minimum setting of the control so that the zcrotor lovvest reading of the control will start at some definite wave length, say the lowest limit of the range which it is desired to cover. For example, with a broadcast receiver it is desirable to start the lowest readng of the dial or control at 200 meters. Furthermore, if the condenser is designed to give a straight line frequency characteristic, this characteristic should not be altered by adjustment of the minimum capacitance.

Since the above dilliculties have been overcome in this invention, it is therefore one of the objects thereof to devise a variable condenser having a novel form of control \vherebv a linear frequency characteristic may be obtained without modifying the shape of the electrode plates.

VAR ABLE" CONDENSER. I

1926. seriaiivo 111,193.

"Itis a' furtherobject of this invention to devise a variable condenser which is provided with 'a' novel means for varying its minimum capacitance without causing a correspondingchange in the maximum capacitance.

,Itis afurther object of this invention to devise afva'i-i able condenser provided with means for varying its minimum capacitance without producing a substantial effect upon its straight line' characteristic.

' It'is a further object of this invention to devise a novel form of cam control for varying the electrodes of a condenser. It is proposed to incorporate such a cam control witha condenser in which both electrodes are movable with respect to the plates.

Further objects of this invention will appear from the following description in which I'have set,fo'rth the-preferred embodiin'ent' of'my invention. It is to be understood that the scope of the invention is to bed e'terminedfrom the appended claims and the 'state .of the prior art.

Referring to 'the drawings:

Figure 1 is a front view of the condenser structure] embodying the principles of this invention.

Fig. 2 is a rear view of the condenser shown "in Fig. 1.

Fig. 3 isa side elevational view showing the condenser applied to an instrument panel.

Fig. 4 is a view illustrating the details of the cam control.

Fig. 5 is a detail view showing the construction for the particular mechanism em ployed for varying the minimum capacitance.

Fig. 6 is a side view of the mechanism shown in'Fig. 5.

-Fig. 7 is a curve diagrammatically illustrating the straight line frequency characteristics of this condenser.

The invention has been incorporated genorally with a variable condenser employing relatively movable electrodes, the positions of which are controlled by means of a rotary shaft. The driving connection between the rotary control shaft and the condenser electrodes preferably includes a cam, the shape of which is such as to cause the electrodes to have relative movement at a rate disproportionate to the rate of rotation of the control shaft. For adjusting the minimum capacitance means are provided for permitting a variable condenser of the general type del electrical capacitance. two electrodes may scribe dfand claimed in United States Patent No. 1,018,399, granted to Roger M. Vise and Ernest G. Danielson, although it is obvious thatthe invention may be incorporated with any type ofcondenser or other tuning device employing relatively movable electrodes. The condenser of the type illustrated compigises a .pair of relatively movable electrodes l0.which are rotatably mounted upon spin- T dies-.11, the spindles being suitably mounted upon an insulating base 12. .Each electrode is constructed of a plurality of spaced plates 13 which are adapted to interleave the plates ofthe other electrode, thereby providing an Connections to the be made thru the binding posts 15 or tabs-1 6 which are electrieally connected to the respective electrodes tlhru flexible conductors 17. In :order to 5 cause the electrodesito rotate simaltaneously in opposite directions, each electrode is provided with a'gear 18 rotatable with the electrode' and meshing with alight gear. provided upon the other electrode. For controlling movement of the electrodes there is provided a control shaft 1!) which is journaled withinthe base 12 and may project thru an instrument panel 20 and receive a. control knob or dial 21.

:lVith the condenser as described above, if

i. the control shaft 19 were mechanically connected with the electrodes as by means of a gear so that angular movement of the control shaft would cause proport onal rotary movement of the electrodes, then the condenser would not have a straight line frequency chara teristic. In other words, if the'condenser were used with a standard inductance, the frequency would not vary at a linear function'of angular movement of the control shaft. Instead of attempting to secure this result by shaping the outlines of the electrode plat-es I have provided a simple form of mechanical drive between the control shaft and one of the electrodes whereby movement of the control shaft will result in a disproportionate movement of the electrodes. Thus there has been provided a lever 23 which is provided with a pivotal connection 24- to the base 12. the piv- ()tal connection being at a point remote from one of the electrode axes. The free end of this lever is preferably provided with a bent portion 25 and has its end operatively secured by means of a connection 26 to one of the electrode gears 18. By means of this connection rocking movement of the lever 23 will impart rotary movement to the electrodes. The bent portion 25 serves to prevent interference of the shaft 19 with the movement of the lever 23. For rocking the lever 23 there is provided a cam 27 which is fixed to the end of the control shaft 19 and.

is provided with a spiral cam groove '28 which engages a pin 29 secured to the intermediate portion of the lever 23. The cam groove 28 is out upon such a.- curve that when the condenser is employed with a given standard inductance it will have a characteristic curve of the type desired which in the particular instance is a straight line frequency characteristic. In other words, the cam is so shaped that for given angular movement of the control shaft the electrodes will have relatively greater movement when near the maximum limit of their capacitance than when near the minimum limit. The groove 28 also serves'xanother useful purpose in that it limits rotational movement of the control shaft 19,1 which in case shown is approximately the particular In practice the dial21 or other 360 degrees indicating device may be the shaft 19.

The connection 26 between the leverj23- and one ofthe gears 18 has been so designed that the minimum ca )acitance of thecondenser may be adjuste without affectirigthe range of movement of the control shaft. and without causing a substantial change injtbe characteristic curve for the condenser. Thus the lever 23 and the gear 18 are provided with slots 31 and 32 respectively in order to receive the adjustable pin 33. This pm may by suitable means such as washers 34 and '35 secured to its ends. For adjusting the position of the pin 33 there is provided a plate 37 secured to one face of the disc 18 as by means of a pin 38, and which is provided with a threaded portion 39 for receiving the adjusting screw 40. Rotation of the screw 40 serves to force the pin 33 towards the center of the gear 13, while a compression spring 41 is provided to engage the opposite side of the pin 33 for returning the same upon rotation of the screw 40 in the opposite direction. A flange 42 may bepro; vided upon the pin 33 and interposed between the lever 23 and the plate 37 for The slots 31 and 32 are located in their respective elements in such a manner that when the controlsha ft 19 is turned to its maximum value the slots will both be aliued with each other and with the axis of the pivotal connection 24 of the lever 23. Thus if the adjusting screw separating the same.

graduated in even spaces between the hunts of movement of be retained in operative .position is'turncd while the lever is in this posi tion no movement (stow. electrodes will-0ccur'since the slots are both alined. However. when the control shaft is'turned to its minimum position then the two slots will be disposed at an angle toeach other and movement. of the pin 33 by adjustment of the screw it) will serve to rotate the gear 18 and the electrodes while the lever 23 and shaft 19 remain stationary.. -This arrangement affords a convenient means for adjust ing the minimum capacitance of the condenser without changing the limit of .movement of the control shaft. i

The effect of this adjustmentis' illustrated in Fig. T in .whiclrthe straight-line characteristic curve has been shown as plotted bet-ween. angular movement of the control shaft. and the frequency of: the circuit with which the condenser is employed. For ex- 11lll1)l(.', lf the condenser is setasoithat iits minimum capacitance is as small as-possible and incorporated with a radio receiving set the rangemf tuning'-may 'tfor example cover a frequency from 175 to 550 meters, depending upon the electrical characteristics of the circuit. Now if for example it is desired to start the tuning range with 200 meters instead of 175 meters then the screw 40 is adjusted until the minimum capacitance has been increased sufficiently to tune the circuit to 200 meters with the dial setting at zero. Then for full movement of the control shaft the condenser will tune from 200 to 550 meters as shown by the dotted curve of Fig. 7. It will also be noted that this dotted curve is also for all practical purposes a straight line, showing that adjustment of the minimum capacitance has not changed the straight line characteristic for the condenser. This result follows from the fact that. the cam 27 is relied upon to obtain the disproportionate movement between the control shaft and the electrodes.

in order to provide a frictioning device to prevent m vement of the cam thru the weight of the electrodes and during adjustment of the screw 40, there is provided a leaf spring -14, suitably mounted upon the base 12 by means of an adjustable screw whereby the cam is frictionally pressed into engagement. with the adjacent face of the base 12. A connection tab 46 may also be provided for grounding the cam, control shaft 19 and lever 23.

I claim:

1. variable condenser comprising relatively movable electrodes, at least one of said (let-trodes being rotatable about a given axis. a rotatable control shaft, :1 pivoted actuating lever, means connecting said shaft and lever whereby said lever is rocked upon rotation of the shaft, a member rotatable with said one electrode, means connecting said member and lever whereby the rocking movement of= the leverrimparts rotary movement to said oneelectrode, said means comprising a pin, means-for adjusting the position of said pin with respect to said lever and member, and means for cons'training'thc movement of said pin to definite paths with respect, to said lever and member,-said:'paths being substantiallyparallel when the elec trodes .oceupy-a position =for maximum? capacitance but .being. intersecting when the electrodes occupy otherrelative positionsr -;2.= A- :variable condenser comprising-relativelymovable electrodes, means including a rotatable-shaft for varying-the relative positioniof saidelectrodes whereby the capacitancc. between i the same is-variedbetween maximum and-minimum values,1the angular motion of saidshaft having substantially a-stna-ight l-inechar'acteristic urvenvi'th respecteto ;freque'ney iwhen the condenser .is shunted acrossa given rinductancc, and means. 'fo r ivarying the minimum; capacitance value of? thecon'denser whilezmaintamin the characteristic; cu rvesubstantially 'stnaiglitp 3. A variable condenser comprising a pair of relatively movable electrodes, a rotatable control shaft, means including a cam having a nondeformable cam surface for effecting relative movement between said electrodes upon rotation of said control shaft, means for limiting the rotary motion of the control shaft between fixed limits corresponding to maximum and minimum capacitance values, and means for varying the minimum capacitance value of the condenser while maintaining the maximum capacitance value substantially constant.

4. A variable condenser comprising a pair of relatively movable electrodes, means including a movable cam having a non-deformable cam surface for effecting relative movement between the electrodes upon rotation of the shaft whereby the capacitance of the condenser may be varied between maximum and minimum limits, and means for adjusting the minimum capacitance of the condenser without affecting the maximum capacitance.

5. A variable condenser comprising a pair of relatively movable electrodes, means iiicluding a movable cam having a non-deformable cam surface for effecting relative movement between the electrodes upon rotation of the shaft whereby the capacitance of the condenser may be varied between maximum and minimum limits, and means for adjusting the range of movement of the electrodes for a given movement of the cam.

G. A variable condenser comprising a pair of relatively movable electrodes, a control shaft having limited rotary motion in either direction, means including a cam connecting said control shaft and at least one of the electrodes for moving the same relative to the other electrode whereby the capacitance of the1 -condenser::may 'be varied between maximum :andminimum limits a-nd means in addition 'to saidieam. for adjusting the value [of the minimum-capacitance 'between said el'eetrodes while maintaining-the maximum capacitance substantially Constant.

.'7-. aMta-riahle condenser comprising'a pair oft-relatively .mova'ble electrodes, :a control shaftihaviing limited rotary motion in either direction, means including-a eam connecting said-control s'h a'ft andiat least oneE-ofjthe electrodes for moving the same relative to the other electrode whereby the capacitance of the' condenser 'may be varied between maximum and "min-imum' limits,- and means in addition to said cam :andforming a part of saidconnecting means Ifor $21djustingihe minimum-capacitance of the condenser.

8. A'variabletuningdevice comprising an electrical element rotatable betweendefinite limits, an arm xnember. adapted 'to be oscil lated, 'a member rotatable with" said element, a pin and :slotconnection between saidmem bers, :and; means 1 fdr adjusting s'a-id pin-J new-1.020

l. 9. A variable tuning device comprising an electrical element rotatable between d finit limits, a'pivetal arm adapted to be Oscillated, a'member rota-tableavith said element, a slot in said .arm, a pin adjustably secured to said member and engaging said slot, said slot in oneposition of said member corresponding toonelimiting position of said element extending-radially with respect to the axis of rotation of said element, and in the other limiting position extending in a direction which as not radial with respect to the axis of notation @of. said element.

10. A variable tuning device comprising a rotatable electrical element, means including a rotatable control shaft for etlecting moveinents of-:said-elei11ent, said means also ineluding aipivoted lever serving to transmit motion :and means for adjusting the mechanical advantage of said lever. lm-testimony whereof, I have hereunto set my hand.= Y

515mm G. DANIELSON. 

